1. Field of the Invention
The present invention generally relates to a method and system for inserting aircraft fuel tanks. The invention particularly relates to a method and system for providing nitrogen-enriched air (NEA) to aircraft fuel tanks using multiple air separation modules (ASMs). The ASMs employ membranes having different permeabilities and selectivities which are particularly selected to meet the varying NEA needs of the aircraft performance requirements.
2. Description of the Related Art
It is generally recognized that fuel vapors in an enclosed area such as a fuel tank may result in flame propagation or even an explosion if sufficient oxygen is present. The threat of an explosion, however, can be substantially reduced if the oxygen concentration in the fuel tank is lowered to 9% by volume or less.
Due to the risk of an explosion, some vehicles, particularly aircrafts, have been equipped with on-board inert gas generating systems (OBIGGS). The OBIGGS are intended to provide a supply of nitrogen or nitrogen-enriched gas to fill the vapor space or ullage in the fuel tank in order to lower its oxygen content and thereby reduce the possibility of an explosion.
Various OBIGGS have been proposed in the art. However, there remains a continuing need in the art for OBIGGS that have reduced size, weight, and operating cost, but yet can provide a sufficient amount and purity of NEA to inert, for example, aircraft fuel tanks during a variety of different operating conditions.